PROBE TUNING ON THE INOVA 400
JB Stothers NMR Facility
Materials Science Addition 0216
Department of Chemistry
Western University
1. INTRODUCTION ............................................................................1
1.1. About these Notes and Related Notes ...............................................1
2. ABOUT PROBE TUNING ON THE INOVA 400 .....................................1
2.1.
2.2.
2.3.
2.4.
What is Probe Tuning? .....................................................................1
Capacitor Sticks ...............................................................................2
Tune and Match Capacitors ..............................................................2
Tuning Values for Some NMR Nuclei on the Inova 400 ........................3
3. PROBE TUNING PROCEDURE ON THE INOVA 400 .............................4
3.1. Probe Tuning on the Inova 400 with a Capacitor Stick ........................4
3.2. Probe Tuning on the Inova 400 with no Capacitor Stick ......................8
3.3. Re-tuning the Probe on the Inova 400 .............................................10
Probe_Tuning_on_the_Inova400_2.0.odt
Jul. 14, 15
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1. INTRODUCTION
1.1. About these Notes and Related Notes
These notes describe how to tune the NMR probe on the Inova 400 in order to perform NMR experiments on
nuclei other than 1H, 13C, 19F or 31P. All NMR active nuclei besides those four nuclei are referred to as “odd
nuclei”. Common odd nuclei studied in the NMR facility include, but are not limited to, 2H, 11B, 29Si, and 77Se,
and odd nuclei NMR experiments can be performed on either of the Inova spectrometers. Once you have
chosen your spectrometer, you should consult additional notes as described in Table 1.1.
Table 1.1. Required and Recommended Notes
If you would like to…
Then you …
…must consult these notes
…should consult these notes
Perform a 1D odd
nucleus NMR experiment
on the Inova 400 or 600
• NMR Sample Preparation
• Reserving NMR Time using FACES
• Basic Operation of the Inova 400 and
600
• Retrieving NMR Data
• Processing 1D NMR Spectra using
VNMRJ
Perform a 2D NMR
experiment involving odd
nuclei on the Inova 400
or 600
• NMR Sample Preparation
• Reserving NMR Time using FACES
• Basic Operation of the Inova 400 and
600
• Retrieving NMR Data
• Processing 2D NMR Spectra using
VNMRJ
2. ABOUT PROBE TUNING ON THE INOVA 400
2.1. What is Probe Tuning?
Each NMR active nuclear isotope resonates at a specific frequency. In order to obtain an NMR
spectrum, radio-frequency (rf) pulses are applied to the sample at the appropriate frequency for that nucleus
(eg. applied at 399.762 MHz for 1H on the Inova 400). The correct frequencies of the pulses are generated by
the frequency synthesizer of the spectrometer, the magnitude of which is increased by the spectrometer’s
amplifiers. The amplified pulses are applied to the probe and then to the sample via the probe’s rf-coil. In
order for the pulse to get to the sample, the frequency of the probe’s circuit must be “tuned” to match the
frequency of the applied pulse from the spectrometer. If the probe is “out of tune”, the pulse is rejected by the
probe and is not applied to the sample. In order to tune the probe to the correct frequency, we insert a specific
capacitor stick (see section 2.2) and adjust the tune and match capacitors (see section 2.3) appropriately.
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PROBE TUNING
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2.2. Capacitor Sticks
A capacitor is an electrical device that stores electrical charge. In NMR, capacitors are used to change
the frequency of the probe’s circuit; increasing the capacitance within the probe reduces the frequency of the
circuit. In order to tune a specific frequency, the appropriate capacitor must be inserted into the probe.
Agilent achieves this by using different capacitor sticks, which are literally sticks with capacitors stuck onto
the top of a stick.
On the Inova 400, the capacitor sticks have 2 prongs that must be aligned in a specific orientation in
order to be properly inserted into the probe. Once properly aligned, the stick is screwed into the probe and
secured in place. There are 4 unique sticks, labeled 1/4-wave, G0PF, G18PF, and G36PF (see Figure 2.1).
(A)
(B)
(C)
Figure 2.1. (A) A capacitor stick utilized on the Inova 400. (B) The top of a capacitor stick used by the HFCP probe on the
Inova 400, showing the 2 prongs and the capacitor. The prongs must be aligned correctly within the probe in order to
insert the stick. (C) The bottom of 3 of the 4 capacitor sticks used by the HFCP probe on the Inova 400. Each capacitor
stick is labeled on the bottom of the stick. The blue metal portion rotates about the off-white insulator rod, allowing the
stick to be screwed securely into the probe.
2.3. Tune and Match Capacitors
The capacitor sticks provide a coarse adjustment of the probe, but the adjustment is too coarse to
acquire NMR spectra. To provide the fine adjustment needed, the probe contains “tune” and “match” variable
capacitors within the probe. The capacitance of these capacitors, and thus the frequency of the probe’s circuit,
is changed by turning the tune and match knobs that are located on the bottom of the probe. The tune
capacitor alters the “tune value” of the probe. This tune value ranges from 1 to 83 and is displayed on the side
of the probe.
CAUTION: The adjustment of the tune and match capacitors is the most common way in which NMR probes
are damaged. The knobs that adjust the capacitors can only turn a finite way in either direction. Normally,
the knobs will turn smoothly and with little resistance. If you feel resistance when adjusting the tune and
match, DO NOT force the knobs to turn further in that direction as doing so will damage the probe.
The Inova 400 uses what is known as an autoswitchable HFCP probe, which is shown in Figure 2.2. This
probe is a 2-channel probe in which each channel can be simultaneously tuned to 2 different nuclei, thus 4
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PROBE TUNING
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400
nuclei can be studied at one time without manipulating the probe. The first channel, the HF channel, is tuned
to 1H and 19F while the second channel, the CP/X-CHANNEL, is usually tuned to 13C and 31P. In order to
independently tune each nucleus, the tune knob, which controls the tune capacitor, can slide up into the UP
position or slide down into the DOWN position. For the HF channel, 19F is tuned with the tune knob in the
DOWN position and 1H is tuned with the tune knob in the UP position. For the CP channel, 13C is tuned with
the tune knob in the DOWN position and 31P is tuned with the tune knob in the UP position. In order to tune
nuclei other than 13C or 31P, the appropriate capacitor stick must be inserted and the probe is usually tuned with
the tune knob in the DOWN position.
(A)
(B)
(C)
Tune
value
CP/X-CHANNEL
tune knob
Capacitor
stick
HF channel
tune knob
HF channel
match knob
CP/X-CHANNEL
match knob
Figure 2.2. The bottom of the HFCP probe used on the Inova 400. (A) Displayed are the tune value, capacitor stick, tune
and match wands for the HF channel (red) and for the CP/X-CHANNEL (green). (B) The tune control can be in either the
up or down position. In the down position, turning the tune wand will tune 19F for the HF channel and 13C for the CP/XCHANNEL in 4-nucleus mode (i.e. when the ¼-wave capacitor stick is inserted). Turning the green (CP/X- CHANNEL)
tune knob in the down position also changes the tune value. (C) The tune control is in the up position, which is used to
tune 1H for the HF channel and 31P for the CP/X- CHANNEL when in 4-nucleus mode.
2.4. Tuning Values for Some NMR Nuclei on the Inova 400
The table below displays the appropriate capacitor stick and tune value for several commonly studied NMR
nuclei in the NMR facility.
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Table 2.1. Tune Values and Capacitor Sticks for Some Commonly Studied NMR Nuclei on the Inova 400
Isotope
Frequency, MHz
Capacitor Stick
Tune Value
2
H
61.3663
G0
20
Li
155.354
None
76
11
B
128.255
None
77
13
C
100.53
1/4-wavea
77
13
C
100.53
Nonea
33
15
N
40.5117
G36
33
29
Si
79.4214
G0
51
31
P
161.822
1/4-wavea
77
31
P
161.822
Nonea
76
59
Co
94.4017
None
10
77
Se
76.2612
G0
47
113
Cd
88.6897
G0
64
119
Sn
149.085
None
73
125
Te
104.782
None
68
195
Pt
85.795
G0
66
a
On the Inova 400, 13C and 31P can both be tuned at the same time using the ¼-wave stick. If 13C or 31P can not be tuned
sufficiently for your sample, you can switch to “single-resonance” mode by removing the capacitor stick completely.
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3. PROBE TUNING PROCEDURE ON THE INOVA 400
3.1. Probe Tuning on the Inova 400 with a Capacitor Stick
On the Inova 400, for nuclei with frequencies less than about 90 MHz, the probe must be tuned with a
capacitor stick inserted (see Table 2.1). For nuclei with frequencies greater than 90 MHz, the probe must be
tuned without a capacitor stick inserted. In this case, the tuning method is slightly different (follow directions
provided in section 3.2). The instructions in this section and in section 3.2 assume that the user is familiar
with the basic operation of the Inova spectrometers. If not, please read the “Basic Operation of the Inova 400
and 600” notes and obtain Inova spectrometer training first.
1) Insert your sample.
2) Disconnect the thin cable in front of the filter and connect it to the connector labeled “PROBE” on the
magnet leg.
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PROBE TUNING
ON THE INOVA
(A)
400
(B)
Disconnect here
Figure 3.1. (A) The cable for the CP/X-channel on the Inova 400. The cable must be disconnected in front
of the filter. (B) The TUNE INTERFACE on the face of the magnet leg. The cable must be connected to the
"PROBE" port on the TUNE INTERFACE.
3) Remove the capacitor stick by turning the blue metal part of the stick clockwise until the stick releases.
Support the stick to prevent the stick from crashing onto the floor.
4) Consult Table 2.1 to find the appropriate capacitor stick for your nucleus of interest.
a)
Gently and slowly insert the appropriate capacitor stick into the probe until you feel resistance.
b) While very gently pushing the stick upwards, slowly rotate the stick in some direction.
c)
When the prongs are properly aligned, you will feel the stick move up about 1 cm and you will no
longer be able to rotate the stick.
d) Screw the stick into the probe by turning the metal part of the stick counterclockwise.
CAUTION: The prongs of the capacitor sticks used on the Inova 400 are very fragile and are thus easily
damaged. Be very gentle and do not force the capacitor stick.
5) Consult Table 2.1 to find the appropriate tune value for your nucleus of interest.
6) With the CP/X-CHANNEL tune knob in the DOWN position, turn the tune knob in the appropriate
direction until the correct tune value is displayed on the probe (see Figure 2.2 for a picture of the tune
value).
TIP: Hold the CP/X-CHANNEL match knob still with one hand while turning the tune knob with the other.
7) Enter “qtune” in VnmrJ’s command line.
QTune.
This command brings up the tuning interface known as
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PROBE TUNING
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Figure 3.2: The default QTune parameter panel.
8) In the drop-down list next to Tune frequency, select your desired nuclear isotope. The frequency will
automatically update after selecting the nucleus.
9) In the field window next to Span, input 50 and hit the enter key.
10) From the drop-down list next to # Points, select 1024.
11) Click on
12) Click on
.
. The following should appear in the Graphics Display screen (Figure 3.2).
Desired
frequency
Match line
Tuning dip; actual
frequency
Figure 3.3. The QTune window used to tune the probe to some chosen nucleus. The dip is the current
frequency of the channel. The match knob will move the dip upwards or downwards while the tune knob will
move the dip left or right. The goal is to adjust the match and tune knobs iteratively until the dip is centred
about the vertical pink line and also touches the match line.
13) Turn the match knob on the CP/X-CHANNEL in some arbitrary direction; the dip will move upwards or
downwards (as well as left or right; ignore the left and right). If the dip moves upwards, reverse the
direction of the match knob. Continue turning the match knob until the dip is near the match line.
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PROBE TUNING
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Figure 3.4. The QTune window after initial adjustment of the match knob. The tuning dip is very close to the
horizontal match line.
CAUTION: The match knob can only turn a finite number of times in either direction. If you feel resistance
when turning the match knob, DO NOT force it to turn further. Doing so will damage the probe.
14) With the CP/X-CHANNEL tune knob in the DOWN position, hold the match knob still with your weak
hand. Turn the tune knob in some arbitrary direction; the dip will move left or right. If the dip moves
away from the vertical centre line, reverse the direction of the tune knob. Continue turning the tune knob
until the dip is centred about the vertical centre line. As the dip moves left or right, the dip may move
upwards away from the bottom match line; do not worry about that at this point.
CAUTION: The tune knob can only turn a finite number of times in either direction. If you feel resistance
when turning the tune knob, DO NOT force it to turn further. Doing so will damage the probe.
15) Iteratively adjust the match and tune (in the DOWN position) knobs until the dip is aligned in the centre
and also with the match line.
Figure 3.5. The QTune window after iteratively adjusting the tune and match knobs.
16) In the window to the right of “Span”, input “5”, followed by enter. Iteratively make fine adjustments of
the match and tune (in the DOWN position) until no further improvements can be made.
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PROBE TUNING
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Figure 3.6. The QTune window after decreasing the span to 5 MHz and making fine adjustments of the tune
and match knobs.
17) Click on
18) Click on
.
.
19) Disconnect the cable from the PROBE connection on the magnet leg and re-connect the cable to the filter.
The probe is now tuned and you can start your experiment.
3.2. Probe Tuning on the Inova 400 with no Capacitor Stick
On the Inova 400, for nuclei with frequencies greater than 90 MHz, the probe must be tuned without a
capacitor stick inserted. The instructions in this section assume that the user is familiar with the basic
operation of the Inova spectrometers. If not, please read the “Basic Operation of the Inova 400 and 600”
worksheet and obtain Inova spectrometer training first.
1) Follow steps 1 through 12 of section 3.1, except do not insert a capacitor stick (i.e. skip step 4).
2) Slide the CP/X-CHANNEL tune knob up and hold the tune knob in the UP position. You should feel the
tune knob engage, but you may have to slightly turn the tune knob to do so.
3) With the CP/X-CHANNEL tune knob in the UP position, turn the tune knob in some arbitrary direction;
the dip will move left or right. If the dip moves away from the vertical pink line, reverse the direction of
the tune knob. Continue turning the X-CHANNEL tune knob in the UP position until the dip is centred
about the vertical pink line. As the dip moves left or right, the dip may move upwards from the bottom
match line; do not worry about that at this point.
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PROBE TUNING
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Figure 3.7: The QTune window after initial adjustment of the CP/X-CHANNEL tune knob in the UP position.
CAUTION: The tune knob can only turn a finite number of times in either direction. If you feel resistance
when turning the tune knob, DO NOT force it to turn further. Doing so will damage the probe.
4) Iteratively adjust the match and tune (in the UP position) knobs until the dip is aligned in the centre and
also with the match line.
Figure 1: The QTune window after iterative adjustment of the CP/X-CHANNEL tune knob in the UP position
and the CP/X-CHANNEL match knob.
5) In the window to the right of “Span”, input “5”, followed by enter. Iteratively make fine adjustments of
the match and tune (in the UP position) until no further improvements can be made.
Figure 2: The QTune window after iteratively fine tuning the CP/X-CHANNEL tune knob in the UP position
and the CP/X-CHANNEL match knob.
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PROBE TUNING
6) Click on
.
7) Click on
.
ON THE INOVA
400
8) Disconnect the cable from the PROBE connection on the magnet leg and re-connect the cable to the filter.
The probe is now tuned and you can start your experiment.
3.3. Re-tuning the Probe on the Inova 400
After completion of your experiment, the probe must be tuned back to
13
C/31P. This procedure is slightly
different than the procedure used to tune odd nuclei.
1) Insert the default CDCl3 sample.
2) Read in a PROTON experiment.
3) Go to the Acquire panel, Channels page.
4) In the space for channel 3, under the word Decouple, input “P31”, then hit the enter key.
5) Go to the Start panel and click on
.
6) Remove the capacitor stick (if applicable) and insert the ¼-wave capacitor stick.
7) Disconnect the thin cable in front of the filter and connect the cable to the connector labeled “PROBE” on
the magnet leg.
8) With the green CP/X-CHANNEL tune knob in the DOWN position, turn the tune knob until the tune value
on the probe reads 77.
9) On the magnet leg, next to the buttons labeled “CHAN”, press the “+” button twice to select channel 2. A
number will be displayed in the TUNE INTERFACE window.
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PROBE TUNING
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10) Turn the X-CHANNEL match knob in some arbitrary direction. If the number displayed in the TUNE
INTERFACE increases, or you feel resistance, reverse the direction you are turning the knob. Continue
until the number displayed reaches a minimum. Note: You may have to turn the match direction many
times before the number displayed changes.
11) On the magnet leg, next to the buttons labeled “CHAN”, press the “+” button once to select channel 3.
12) Slide the X-CHANNEL tune knob into the UP position (you will have to hold it up). With the tune knob
in the UP position, turn the tune knob in some arbitrary direction. If the number displayed in the TUNE
INTERFACE increases, or you feel resistance, reverse the direction you are turning the tune knob.
Continue until the number displayed reaches a minimum. Note: You may have to turn the tune knob many
times before the number displayed changes.
13) On the magnet leg, next to the buttons labeled “CHAN”, press the “─” button once to select channel 2.
14) Repeat steps 10 through 13 until the number displayed when channel 2 is selected is less than 40 and the
number displayed when channel 3 is selected is less than 375.
15) On the magnet leg, next to the buttons labeled “CHAN”, press the “─” button twice/thrice to select
channel 0.
16) Disconnect the cable from the PROBE connection on the magnet leg and re-connect the cable to the filter.